Slurry, polishing fluid set, polishing fluid, and substrate polishing method using same

ABSTRACT

A slurry includes abrasive grains and water, wherein the abrasive grains include tetravalent cerium hydroxide particles and produce light transmittance of at least 50%/cm for light with a wavelength of 500 nm in an aqueous dispersion with the content of the abrasive grains adjusted to 1.0 mass %. A polishing liquid includes abrasive grains, an additive and water, wherein the abrasive grains include tetravalent cerium hydroxide particles and produce light transmittance of at least 50%/cm for light with a wavelength of 500 nm in an aqueous dispersion with the content of the abrasive grains adjusted to 1.0 mass %.

TECHNICAL FIELD

The present invention relates to a slurry, a polishing liquid set, apolishing liquid and a substrate polishing method using the same. Inparticular, the present invention relates to a slurry, a polishingliquid set, a polishing liquid and a substrate polishing method usingthe same, for semiconductor use.

BACKGROUND ART

Highly precise and sophisticated polishing of substrate surfaces isnecessary in many cases including for substrates such as glasses forflat panel display, magnetic disks and silicon wafers for semiconductor,and insulating films, metal layers, barrier layers and the like whichare formed in semiconductor device manufacturing steps. Such polishingis usually carried out using a polishing liquid comprising abrasivegrains including silica, alumina, zirconia or cerium oxide, for example,according to the purpose of use.

The progressively high integration and micronization in semiconductordevice manufacturing steps in recent years is further reducing thepermissible sizes of scratches generated on the surface to be polishedduring polishing. It is therefore becoming more difficult to reducescratches.

A variety of different abrasive grains are used to reduce scratches. Forexample, polishing liquids widely used for polishing of inorganicinsulating films such as silicon oxide films in semiconductor devicemanufacturing steps are polishing liquids comprising cerium oxide asabrasive grains (see Patent document 1, for example). Cerium oxide has alower hardness than silica or alumina, and produces fewer scratches onsurfaces to be polished, and it is therefore widely used as abrasivegrains.

It is also often attempted to reduce the abrasive grain particle sizesin order to reduce scratches. However, reducing the abrasive grainparticle sizes lowers the mechanical effect of the abrasive grains, andthus reduces the polishing rate. Therefore, it is attempted, withabrasive grains used in the prior art, to achieve both increasedpolishing rate and reduced scratches by controlling the particle sizesof the abrasive grains, but it is still extremely difficult to reducescratches. This problem is being studied with the aim of achieving bothincreased polishing rate and reduced scratches by using a polishingliquid comprising tetravalent cerium hydroxide particles (see Patentdocument 2, for example), and research is also being conducted onmethods for producing tetravalent cerium hydroxide particles (see Patentdocument 3, for example).

In order to achieve flat polishing of inorganic insulating films withirregularities, an excellent polishing selective ratio of the film to bepolished, such as a silicon oxide film, with respect to the stopperfilm, such as a silicon nitride film (polishing rate ratio: polishingrate for film to be polished/polishing rate for stopper film) isrequired for polishing liquids comprising such tetravalent ceriumhydroxide particles. Various additives has been added to polishingliquids and investigated in order to solve this problem. For example,polishing liquids that can improve the flatness of polished surfaceshave been proposed, wherein anionic additives are added to the polishingliquids for a satisfactory polishing rate for silicon oxide films withessentially no polishing of silicon nitride films (namely, havingpolishing selectivity of silicon oxide films to silicon nitride films)(see Patent document 4, for example).

A variety of additives have thus been investigated in order to adjustthe properties of polishing liquids, but depending on the additivesused, there has sometimes been a trade-off between the effect obtainedby the additives and reduction in polishing rate.

CITATION LIST Patent Literature

[Patent document 1] Japanese Unexamined Patent Application PublicationHEI No. 9-270402

[Patent document 2] International Patent Publication No. WO 02/067309

[Patent document 3] Japanese Unexamined Patent Application PublicationNo. 2006-249129

[Patent document 4] Japanese Unexamined Patent Application PublicationNo. 2002-241739

SUMMARY OF INVENTION Technical Problem

Against such problems, conventionally, changing the types of additivesor reducing the amounts of additives is generally attempted in order toachieve both polishing rate and the functions obtained by the additives,but there have been limits to the functions obtained by the additives.In recent years it is being required for polishing liquids to achieveeven higher levels for both the polishing rate and the addition effectsof additives.

The present invention solves the problems described above, and it is anobject thereof to provide a slurry that allows polishing of a film to bepolished at an excellent polishing rate. It is another object of theinvention to provide a slurry that can yield a polishing liquid thatallows the addition effects of additives to be obtained while alsoallowing polishing of a film to be polished at an excellent polishingrate.

It is yet another object of the invention to provide a polishing liquidset and a polishing liquid that allow the addition effects of additivesto be obtained while also allowing polishing of a film to be polished atan excellent polishing rate.

It is yet another object of the invention to provide a polishing methodusing the polishing liquid set or the polishing liquid.

Solution to Problem

The present inventors have conducted diligent research toward increasingthe speed of polishing using polishing liquids for semiconductor, and asa result they have found that, in a slurry comprising tetravalent ceriumhydroxide particles as the abrasive grains, it is possible to inhibitreduction in polishing rate when additives have been added, by usingabrasive grains that can increase the light transmittance to light of aspecific wavelength in an aqueous dispersion comprising the abrasivegrains in a specific amount, and have completed this invention.

More specifically, the slurry of the invention comprises abrasive grainsand water, the abrasive grains including tetravalent cerium hydroxideparticles and producing light transmittance of at least 50%/cm for lightwith a wavelength of 500 nm in an aqueous dispersion with the content ofthe abrasive grains adjusted to 1.0 mass %.

According to such a slurry, it is possible to inhibit reduction in thepolishing rate for films to be polished (such as inorganic insulatingfilms) when additives have been added to the slurry, thus allowing bothan excellent polishing rate and addition effects of additives than witha conventional polishing liquid. In addition, it is also possible toaccomplish polishing of films to be polished with excellent polishingrate when the slurry is used for polishing without addition ofadditives.

The mean particle size of the abrasive grains is preferably 1-150 nm.This will allow an even more excellent polishing rate to be obtained forfilms to be polished.

The pH of the slurry is preferably 2.0-9.0. This will allow an even moreexcellent polishing rate to be obtained for films to be polished.

The content of the abrasive grains is preferably 0.01-15 mass % based onthe total mass of the slurry. This will allow an even more excellentpolishing rate to be obtained for films to be polished.

The content of the tetravalent cerium hydroxide particles is preferably0.01-10 mass % based on the total mass of the slurry. This will allow aneven more excellent polishing rate to be obtained for films to bepolished. From the same viewpoint, the abrasive grains are preferablycomposed of tetravalent cerium hydroxide particles.

The polishing liquid set of the invention comprises constituentcomponents of a polishing liquid separately stored as a first liquid andsecond liquid, so that the first liquid and second liquid are mixed toform the polishing liquid, wherein the first liquid is theaforementioned slurry, and the second liquid comprises an additive andwater. This will allow a polishing liquid with even more excellentstorage stability to be obtained.

In the polishing liquid set of the invention, the mean particle size ofthe abrasive grains in the polishing liquid is preferably 1-200 nm.

In the polishing liquid set of the invention, the ratio of change of themean particle size of the abrasive grains is preferably not greater than30%, before and after mixing the first liquid and second liquid.Specifically, the mean particle size R1 of the abrasive grains in thefirst liquid and the mean particle size R2 of the abrasive grains in thepolishing liquid preferably satisfy the following formula (1). This willallow a polishing liquid set to be prepared which has low change in theparticle size of the abrasive grains before and after mixing the firstliquid and second liquid, therefore even more excellent polishing ratecan be obtained for films to be polished.|R1−R2|/R1×100≤30  (1)

The additive is preferably at least one type selected from amongdispersing agents, polishing rate improvers, flattening agents andselective ratio improvers. This will allow reduction in polishing rateto be prevented while obtaining the effects of each of the additives.

The additives preferably is a vinyl alcohol polymer and/or a vinylalcohol polymer derivative. A vinyl alcohol polymer and a vinyl alcoholpolymer derivative exhibit effects of improving the stability of thepolishing liquid, by use in combination with tetravalent ceriumhydroxide particles.

The content of the additive in the polishing liquid is preferably 0.01mass % or greater based on the total mass of the polishing liquid.

The polishing liquid of the invention may be prepared as the one-packpolishing liquid obtained by pre-mixing the first liquid and secondliquid into a single liquid. Specifically, the polishing liquid of theinvention comprises abrasive grains, an additive and water, the abrasivegrains including tetravalent cerium hydroxide particles and producinglight transmittance of at least 50%/cm for light with a wavelength of500 nm in an aqueous dispersion with the content of the abrasive grainsadjusted to 1.0 mass %.

In the polishing liquid of the invention, it is possible to obtain theaddition effects of additives while also accomplishing polishing of afilm to be polished at an excellent polishing rate.

The content of tetravalent cerium hydroxide particles in the one-packpolishing liquid is preferably 0.01-8 mass % based on the total mass ofthe polishing liquid. This will allow an even more excellent polishingrate to be obtained for films to be polished.

The mean particle size of the abrasive grains in the one-pack polishingliquid is preferably 1-200 nm.

The pH of the one-pack polishing liquid is preferably 3.0-9.0. This willallow an even more excellent polishing rate to be obtained for films tobe polished.

The additive in the one-pack polishing liquid is preferably at least onetype selected from among dispersing agents, polishing rate improvers,flattening agents and selective ratio improvers. This will allowreduction in polishing rate to be prevented while obtaining the effectsof each of the additives.

The additive in the one-pack polishing liquid is preferably a vinylalcohol polymer and/or a vinyl alcohol polymer derivative. A Vinylalcohol polymer and a vinyl alcohol polymer derivative exhibit effectsof improving the stability of polishing liquid, by use in combinationwith tetravalent cerium hydroxide particles.

The content of the additive in the one-pack polishing liquid ispreferably 0.01 mass % or greater based on the total mass of thepolishing liquid.

The substrate polishing method of the invention comprises a step ofplacing a film to be polished, of a substrate which has the film to bepolished on its surface, so as to face an abrasive pad, and a step ofpolishing at least a portion of the film to be polished while supplyingthe one-pack polishing liquid between the abrasive pad and the film tobe polished.

The substrate polishing method of the invention also comprises a step ofplacing a film to be polished, of a substrate which has the film to bepolished on its surface, so as to face an abrasive pad, a step of mixingthe first liquid and second liquid of the polishing liquid set to obtainthe polishing liquid, and a step of polishing at least a portion of thefilm to be polished while supplying the polishing liquid between theabrasive pad and the film to be polished.

The substrate polishing method of the invention also comprises a step ofplacing a film to be polished, of a substrate which has the film to bepolished on its surface, so as to face an abrasive pad, and a step ofpolishing at least a portion of the film to be polished while supplyingthe first liquid and second liquid of the polishing liquid set betweenthe abrasive pad and the film to be polished.

According to these substrate polishing methods, it is possible to obtainthe addition effects of additives while also accomplishing polishing ofa film to be polished at an excellent polishing rate. It is alsopossible to accomplish polishing of a film to be polished at higher rateand to greater flatness than with a conventional polishing liquid.

Advantageous Effects of Invention

According to the slurry of the invention it is possible to accomplishpolishing of a film to be polished at an excellent polishing rate thanwith a conventional polishing liquid. In addition, according to theslurry of the invention, it is possible to obtain a polishing liquidthat allows the addition effects of additives to be obtained while alsoallowing polishing of a film to be polished at an excellent polishingrate than with a conventional polishing liquid. According to thepolishing liquid set and polishing liquid of the invention, it ispossible to inhibit reduction in polishing rate for a film to bepolished even when the polishing liquid contains additives, and it istherefore possible to obtain the effects of the additives while alsoallowing polishing of the film to be polished at an excellent polishingrate than with a conventional polishing liquid.

Furthermore, according to the invention, it is easier to obtaindifferent properties required depending on object to be polished, whilemaintaining the property of high-rate polishing of semiconductorsurfaces in wiring formation steps. In addition, according to theinvention, it is possible to accomplish high-rate polishing of a diverserange of substrates by controlling the types of additives.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing the aggregated condition ofabrasive grains when an additive has been added.

FIG. 2 is a schematic diagram showing the aggregated condition ofabrasive grains when an additive has been added.

FIG. 3 is a graph showing the relationship between the content ofpolyvinyl alcohol (PVA) added and polishing rate.

DESCRIPTION OF EMBODIMENTS

An embodiment of the invention will now be explained in detail. Thepolishing liquid of this embodiment can be obtained by mixing a slurry(first liquid) comprising at least water and abrasive grains with anadditive liquid (second liquid) comprising at least an additive andwater. In this embodiment, the polishing liquid and the slurry differ inthe presence or absence of the additive.

(Slurry)

The slurry of this embodiment comprises at least water and abrasivegrains dispersed in the water, wherein the abrasive grains includetetravalent cerium hydroxide particles and produce light transmittanceof at least 50%/cm for light with a wavelength of 500 nm in an aqueousdispersion with the content of the abrasive grains adjusted to 1.0 mass%. The constituent components of the slurry of this embodiment will nowbe explained in detail.

The slurry of this embodiment includes tetravalent cerium hydroxideparticles as the abrasive grains. The tetravalent cerium hydroxideparticles may be obtained, for example, by mixing a tetravalent ceriumsalt and an alkali solution. This technique is explained in detail inJapanese Unexamined Patent Application Publication No. 2006-249129, forexample.

Any known tetravalent cerium salt may be used without any particularrestrictions, with specific examples including Ce(SO₄)₂, Ce(NH₄)₂(NO₃)₆and Ce(NH₄)₄(SO₄)₄.

Known alkali solutions may be used, without any particular restrictions.Specific examples of bases to be used as alkaline sources in the alkalisolution include organic bases such as ammonia, triethylamine, pyridine,piperidine, pyrrolidine, imidazole and chitosan; and inorganic basessuch as potassium hydroxide and sodium hydroxide, among which ammonia ispreferred in that it is widely used in industry and is readily andcheaply available.

The method described above yields a suspension of cerium hydroxideparticles. When the obtained suspension contains metal impurities, forexample, the metal impurities may be removed by a method such asrepeated solid-liquid separation by centrifugal separation or the like.A slurry may be obtained by adding water (purified water) as a mediumafter adequate washing of the suspension containing the cerium hydroxideparticles, and/or separation of the cerium hydroxide particles, but thewashed suspension may also be used directly as a slurry withoutseparation of the cerium hydroxide particles.

The method of dispersing the cerium hydroxide particles in the obtainedslurry may be ordinary stirring dispersion, or a homogenizer, ultrasonicdisperser, wet ball mill or the like may be used.

With the abrasive grains used in the slurry of this embodiment, thelight transmittance for light with a wavelength of 500 nm is at least50%/cm in the aqueous dispersion with a content (concentration) of theabrasive grains adjusted to 1.0 mass %. This will inhibit reduction inthe polishing rate even when the additives mentioned below are added tothe slurry, and will make it easier to obtain other properties whilemaintaining the polishing rate. From the same viewpoint, the lighttransmittance is preferably at least 60%/cm, more preferably at least70%/cm, even more preferably at least 80%/cm and especially preferablyat least 90%/cm. The upper limit for the light transmittance is 100%/cm.

Although the reason for which reduction in polishing rate can beinhibited by adjusting the light transmittance of the abrasive grains isnot thoroughly understood, the present inventors conjecture as follows.It is conjectured that the dominant action of tetravalent ceriumhydroxide particles as abrasive grains is chemical function rather thanmechanical function. Therefore, it is conjectured that the number ofabrasive grains contributes to the polishing rate more than the sizes ofthe abrasive grains.

In this regard, in the case of low light transmittance in an aqueousdispersion having an abrasive grain content of 1.0 mass %, the abrasivegrains present in the aqueous dispersion presumably include moreparticles with relatively large particle sizes (hereunder referred to as“coarse particles”). When an additive (such as PVA) is added to a slurrycomprising such abrasive grains, other particles aggregate around thecoarse particles as nuclei, as shown in FIG. 1. As a result, it isconjectured that, the number of abrasive grains acting on the surface tobe polished per unit area (the effective abrasive grain number) isreduced and therefore the specific surface area of the abrasive grainscontacting with the surface to be polished is reduced, whereby thepolishing rate is lowered.

Conversely, in the case of high light transmittance in an aqueousdispersion having an abrasive grain content of 1.0 mass %, the abrasivegrains present in the aqueous dispersion presumably include fewer“coarse particles”. In such cases with a low abundance of coarseparticles, as shown in FIG. 2, few coarse particles available as nucleifor aggregation are present, even when an additive (such as PVA) isadded to the slurry, and therefore aggregation between abrasive grainsis inhibited or the sizes of the aggregated particles are smaller thanthe aggregated particles shown in FIG. 1. As a result, it is conjecturedthat, the number of abrasive grains acting on the surface to be polishedper unit area (the effective abrasive grain number) is maintained andtherefore the specific surface area of the abrasive grains contactingwith the surface to be polished is maintained, whereby the polishingrate is not easily lowered.

According to research by the present inventors, it was found that evenamong polishing liquids having identical particle sizes as measured witha common particle size measuring apparatus, some may be visuallytransparent (high light transmittance) and some visually turbid (lowlight transmittance). This suggests that coarse particles, which producethe effect described above, can contribute to reduced polishing rateeven in slight amounts that cannot be detected with common particle sizemeasuring apparatuses.

It was also found that even repeated filtration to reduce the amount ofcoarse particles does not significantly improve the phenomenon of lowerpolishing rate with addition of additives, and in some cases the effectof improved polishing rate due to light transmittance is not adequatelyexhibited. Then, the present inventors found that this problem can beovercome by using abrasive grains with high light transmittance inaqueous dispersion, by modifying the method for producing the abrasivegrains or the like.

The light transmittance is the transmittance for light with a wavelengthof 500 nm. The light transmittance is measured with a spectrophotometer,and specifically, it may be measured with an U3310 Spectrophotometer(apparatus name) by Hitachi, Ltd., for example.

As a more specific measuring method, measurement is conducted bypreparing a measuring sample (aqueous dispersion) with water dilution orconcentration to an abrasive grain content of 1.0 mass %, placingapproximately 4 mL (where L represents liters, same hereunder) in a 1cm-square cell, and setting the cell in the apparatus. When themeasuring sample is an aqueous dispersion having a light transmittanceof at least 50%/cm in a state with the abrasive grains present atgreater than 1.0 mass %, the light transmittance will be at least 50%/cmeven when the measuring sample is diluted to 1.0 mass %. Therefore,measuring the light transmittance in a state with the abrasive grainspresent at greater than 1.0 mass % allows screening of the lighttransmittance with a convenient method.

The method of controlling the light transmittance will now be explained.The method of altering the light transmittance may be one in which, forexample, mild reaction between a metal salt and an alkali solution takesplace during production of the abrasive grains, for increased lighttransmittance. This can inhibit rapid grain growth and can reduce theproportion of coarse particles in the abrasive grains.

The method of altering the light transmittance may involve, for example,controls of the starting concentrations for the metal salt aqueoussolution and the alkali solution, the mixing rate of the metal saltaqueous solution and the alkali solution, the stirring speed for mixing,or the liquid temperature during mixing. Control of these will now bedescribed in detail.

[Starting Concentrations]

By controlling the starting concentrations of the metal salt aqueoussolution and the alkali solution, it is possible to alter the lighttransmittance. Specifically, the light transmittance tends to be higherwhen the starting concentrations are reduced, while the lighttransmittance tends to be lower when the starting concentrations areincreased. When a nitrogen-containing heterocyclic organic base or thelike exhibiting weak basicity is used as the base, the startingconcentration of the alkali solution is preferably higher than whenammonia is used.

The upper limit of the concentration for the metal salt is preferablynot greater than 1.0 mol/L, more preferably not greater than 0.5 mol/L,even more preferably not greater than 0.1 mol/L and especiallypreferably not greater than 0.05 mol/L, from the viewpoint of inhibitingrapid occurrence of the reaction. The lower limit of the content for themetal salt is not particularly restricted from the standpoint of lighttransmittance, but it is preferably 0.01 mol/L or greater in order tominimize the amount of aqueous solution used to obtain the prescribedamount of tetravalent cerium hydroxide particles.

The upper limit of the starting concentration for the alkali solution ispreferably not greater than 25 mol/L, more preferably not greater than20 mol/L and even more preferably not greater than 15 mol/L, from theviewpoint of inhibiting rapid occurrence of the reaction. The lowerlimit of the starting concentration for the alkali solution is notparticularly restricted from the standpoint of light transmittance, butit is preferably 0.1 mol/L or greater in order to minimize the amount ofaqueous solution used to obtain the prescribed amount of tetravalentcerium hydroxide particles.

[Mixing Rate]

By controlling the mixing rate of the metal salt aqueous solution andthe alkali solution, it is possible to alter the light transmittance.Specifically, the light transmittance tends to be higher when the mixingrate is increased, while the light transmittance tends to be lower whenthe mixing rate is decreased. The mixing rate is preferably 0.1 cc/minor greater and preferably not greater than 50 cc/min. However, themixing rate is preferably determined by the starting concentrations, andspecifically, the mixing rate is preferably decreased when the startingconcentrations are high, for example.

[Stirring Speed]

By controlling the stirring speed for mixing of the metal salt aqueoussolution and the alkali solution, it is possible to alter the lighttransmittance. Specifically, the light transmittance tends to be higherwhen the stirring speed is increased, while the light transmittancetends to be lower when the stirring speed is decreased.

As the stirring speed, for example, in the case of a mixing scale inwhich a stirring blade with a total length of 4 cm is used for stirringof a 2 L solution, the rotational speed of the stirring blade (thestirring speed) is preferably 50-1000 rpm. The upper limit for therotational speed is preferably not greater than 1000 rpm, morepreferably not greater than 800 rpm and even more preferably not greaterthan 500 rpm, from the viewpoint of preventing excessive increase in theliquid level. Modifying (for example, enlarging) the mixing scale allowschange to the optimal stirring speed, but so long as it is within therange of about 50-1000 rpm, it is possible to obtain a slurry withsatisfactory light transmittance.

[Liquid Temperature]

By controlling the liquid temperature for mixing of the metal saltaqueous solution and the alkali solution, it is possible to alter thelight transmittance. Specifically, the light transmittance tends to behigher when the liquid temperature is reduced, while the lighttransmittance tends to be lower when the liquid temperature isincreased.

The liquid temperature is preferably within the range of 0-60° C., asthe temperature in the reaction system read upon placing a thermometerin the reaction system. The upper limit for the liquid temperature ispreferably not higher than 60° C., more preferably not higher than 50°C., even more preferably not higher than 40° C., especially preferablynot higher than 30° C. and extremely preferably not higher than 25° C.,from the viewpoint of preventing rapid reaction. The lower limit for theliquid temperature is preferably 0° C. or higher, more preferably 5° C.or higher, even more preferably 10° C. or higher, especially preferably15° C. or higher and extremely preferably 20° C. or higher, from theviewpoint of facilitating progress of the reaction, since a very lowliquid temperature will interfere with progress of the reaction.

The mean particle size R1 of the abrasive grains in the slurry ispreferably in the range of 1-150 nm. The upper limit for the meanparticle size R1 is preferably not greater than 150 nm, more preferablynot greater than 120 nm, even more preferably not greater than 100 nmand especially preferably not greater than 80 nm, from the viewpoint ofreducing the mean particle size in order to increase the specificsurface area of the abrasive grains contacting the surface to bepolished, thereby allowing the polishing rate to be further improved.The lower limit for the mean particle size R1 is preferably 1 nm orgreater, more preferably 2 nm or greater and even more preferably 5 nmor greater, since a certain degree of large mean particle size will tendto facilitate increase in the polishing rate.

In this embodiment, the mean particle size R1 is the secondary particlediameter that can be measured by a photon correlation method, andspecifically, it can be measured using a Zetasizer 3000HS (apparatusname) by Malvern Instruments Ltd. or a N5 (apparatus name) by Coulter.The following is an example of a specific measuring method using aZetasizer 3000HS. The slurry is diluted with water or concentrated to anabrasive grain content of 0.2 mass %, to prepare a measuring sample.Approximately 4 mL of the measuring sample is placed in a 1 cm-squarecell, and the cell is set in the apparatus. Measurement is conducted at25° C. with a dispersing medium refractive index of 1.33 and a viscosityof 0.887 mPa·s, and the value represented by the Z-average size is readas the mean particle size.

The content of the abrasive grains is not particularly restricted, butit is preferably not greater than 15 mass % based on the total mass ofthe slurry, from the viewpoint of helping to avoid aggregation of theabrasive grains. The content of the abrasive grains is preferably 0.01mass % or greater based on the total mass of the slurry, from theviewpoint of facilitating the mechanical effect of the abrasive grains.

It is believed that, among the constituent components in the slurry ofthis embodiment, the tetravalent cerium hydroxide particles contributemost to polishing of inorganic insulating films and the like. Thecontent of the tetravalent cerium hydroxide particles is preferably notgreater than 10 mass % based on the total mass of the slurry, from theviewpoint of helping to avoid aggregation of the abrasive grains. Thecontent of the tetravalent cerium hydroxide particles is preferably 0.01mass % or greater based on the total mass of the slurry, from theviewpoint of allowing the function of the tetravalent cerium hydroxideparticles to be adequately exhibited.

The slurry of this embodiment may employ cerium hydroxide particles incombination with other types of abrasive grains, within a range thatdoes not impair the properties of the tetravalent cerium hydroxideparticles, and specifically, abrasive grains composed of such as silica,alumina or zirconia, for example, may be used. However, from theviewpoint of obtaining an even more excellent polishing rate, theabrasive grains are preferably composed of tetravalent cerium hydroxideparticles, with the preferred content described above.

There are no particular restrictions on the water used in the slurry ofthis embodiment and in the additive liquid described hereunder, butdeionized water or ultrapure water is preferred. The water content isnot particularly restricted and may be the content of the remainderexcluding the other constituent components.

The pH of the slurry is preferably in the range of 2.0-9.0, from theviewpoint of obtaining an even more excellent polishing rate. From theviewpoint of stabilizing the pH of the slurry and minimizing problemssuch as aggregation of abrasive grains due to addition of a pHstabilizer, the lower limit for the pH is preferably 2.0 or greater,more preferably 3.0 or greater and even more preferably 3.5 or greater.Also, from the viewpoint of excellent dispersibility of the abrasivegrains and obtaining an even more excellent polishing rate, the upperlimit for the pH is preferably not greater than 9.0, more preferably notgreater than 8.0, even more preferably not greater than 7.0 andespecially preferably not greater than 6.0.

When the slurry is used directly for polishing, the pH of the slurry ispreferably 3.0-9.0. From the viewpoint of stabilizing the pH of thepolishing liquid and minimizing problems such as aggregation of abrasivegrains due to addition of a pH stabilizer, the lower limit for the pH ispreferably 3.0 or greater, more preferably 4.0 or greater and even morepreferably 5.0 or greater. Also, from the viewpoint of excellentdispersibility of the abrasive grains and obtaining an even moreexcellent polishing rate, the upper limit for the pH is preferably notgreater than 9.0, more preferably not greater than 8.0 and even morepreferably not greater than 7.5, while from the viewpoint of excellentstable dispersibility even with a high abrasive grain concentration, itis especially preferably not greater than 7.0 and extremely preferablynot greater than 6.5.

The pH of the slurry can be measured with a pH meter (for example, aModel PH81 by Yokogawa Electric Corp.). The pH that is used may beobtained by placing an electrode in the slurry after 2-point calibrationusing standard buffer (phthalate pH buffer: pH 4.01 (25° C.), neutralphosphate pH buffer: pH 6.86 (25° C.)), and by measuring the value uponstabilization after an elapse of 2 minutes or more.

Any known pH regulator may be used to adjust the pH of the slurry,without any particular restrictions, and specifically, there may be usedinorganic acids such as phosphoric acid, sulfuric acid or nitric acid;organic acids such as formic acid, acetic acid, propionic acid, maleicacid, phthalic acid, citric acid or succinic acid; amines such asethylenediamine, toluidine, piperazine, histidine or aniline; andnitrogen-containing heterocyclic compounds such as pyridine, imidazole,triazole or pyrazole.

A pH stabilizer is an additive for adjustment to a prescribed pH, and itis preferably a buffer component. The buffer component is preferably acompound with a pKa in the range of ±1.5, and more preferably a compoundwith a pKa in the range of ±1.0, relative to the prescribed pH. Suchcompounds include amino acids such as glycine, arginine, lysine,asparagine, aspartic acid and glutamic acid.

(Polishing Liquid Set)

The polishing liquid of this embodiment may be prepared as a polishingliquid set in which the constituent components of the polishing liquidare separated into and stored as two liquids, the slurry described aboveand an additive liquid comprising additives dissolved in water, so thatthe polishing liquid is produced by mixing the slurry and additiveliquid. The polishing liquid set is used as a polishing liquid by mixingthe slurry and additive liquid at the time of polishing, as describedhereunder. By thus separating and storing the constituent component ofthe polishing liquid into at least two liquids, the storage stability ofthe polishing liquid is improved.

The mean particle size R2 of the abrasive grains in a polishing liquidobtained by mixing a slurry and additive liquid is preferably 1-200 nm.The mean particle size R2 of at least 1 nm will allow a sufficientmechanical effect of the abrasive grains to be obtained. From the sameviewpoint, the lower limit for the mean particle size R2 is morepreferably 5 nm or greater, even more preferably 10 nm or greater andespecially preferably 15 nm or greater. The upper limit for the meanparticle size R2 of the abrasive grains is preferably not greater than200 nm, more preferably not greater than 150 nm and even more preferablynot greater than 100 nm, from the viewpoint of increasing the specificsurface area of the abrasive grains contacting the surface to bepolished, thereby allowing the polishing rate to be further improved.

In the polishing liquid of this embodiment, the mean particle size R2 isthe secondary particle diameter that can be measured by a photoncorrelation method, and for example, it can be measured specificallywith a Zetasizer 3000HS (apparatus name) by Malvern Instruments Ltd. oran N5 (apparatus name) by Coulter. The following is a specific measuringmethod using a Zetasizer 3000HS. After obtaining the polishing liquid bymixing the slurry and additive liquid, the polishing liquid is dilutedwith water or concentrated to an abrasive grain content of 0.2 mass %,to prepare a measuring sample. Next, approximately 4 mL of the measuringsample is placed in a 1 cm-square cell, and the cell is set in theapparatus. Then, measurement is conducted at 25° C. with a dispersingmedium refractive index of 1.33 and a viscosity of 0.887 mPa·s, and thevalue represented by the Z-average size is read as the mean particlesize.

When the mean particle size of the abrasive grains is compared beforeand after mixture of the slurry and additive liquid, the polishingliquid set of this embodiment preferably has a small rate of changethereof. Specifically, the rate of change is preferably not greater than30%, more preferably not greater than 20% and even more preferably notgreater than 10%. A rate of change of not greater than 30% for the meanparticle size of the abrasive grains means that the mean particle sizeR1 and the mean particle size R2 satisfy the following formula (2). Thevalue |R1−R2| represents the absolute value of the difference between R1and R2.|R1−R2|/R1×100≤30  (2)

A polishing liquid comprising abrasive grains dispersed in watergenerally tends to have more aggregation of abrasive grains uponaddition of an additive. In this embodiment, however, aggregation ofabrasive grains can be further inhibited by using abrasive grains thatproduce light transmittance of at least 50%/cm for light with awavelength of 500 nm in an aqueous dispersion with the content of theabrasive grains adjusted to 1.0 mass %, while lowering the rate ofchange of the mean particle size. This embodiment can therefore achieveeven higher levels for the addition effect of additives and the effectof improved polishing rate.

The content of the abrasive grains is preferably 0.01-10 mass % and morepreferably 0.1-5 mass %, based on the total mass of the polishingliquid. The content of the tetravalent cerium hydroxide particles ispreferably 0.01-8 mass % and more preferably 0.1-5 mass %, based on thetotal mass of the polishing liquid.

The pH of the polishing liquid obtained by mixing the slurry andadditive liquid is preferably in the range of 3.0-9.0, from theviewpoint of obtaining an even more excellent polishing rate. From theviewpoint of stabilizing the pH of the polishing liquid and minimizingproblems such as aggregation of abrasive grains due to addition of a pHstabilizer, the lower limit for the pH is preferably 3.0 or greater,more preferably 4.0 or greater and even more preferably 5.0 or greater.Also, from the viewpoint of excellent dispersibility of the abrasivegrains and obtaining an even more excellent polishing rate, the upperlimit for the pH is preferably not greater than 9.0, more preferably notgreater than 8.0 and even more preferably not greater than 7.5, from theviewpoint of excellent stable dispersibility even with a high abrasivegrain concentration, it is especially preferably not greater than 7.0and yet more preferably not greater than 6.5.

The pH of the polishing liquid can be measured in the same manner as thepH of the slurry. Also, the same pH regulator and pH stabilizer, usedfor adjustment of the pH of the slurry, may be used for adjustment ofthe pH of the polishing liquid.

(Additive Liquid)

The polishing liquid obtained using the slurry of this embodiment allowsan especially excellent polishing rate to be obtained for inorganicinsulating films (for example, silicon oxide films), and is thereforeespecially suitable for polishing of substrates with inorganicinsulating films. Such a polishing liquid can be obtained by adding anadditive liquid, containing additives that impart other functions, tothe slurry.

An additive used in the additive liquid may be a known additive withoutany particular restrictions, such as a dispersing agent that increasesthe dispersibility of the abrasive grains, a polishing rate improverthat increases the polishing rate, a flattening agent (a flatteningagent that reduces irregularities on the polished surface afterpolishing, or a global flattening agent that improves the in-planeuniformity of the substrate after polishing), or a selective ratioimprover that improves the polishing selective ratio with respect tostopper films such as silicon nitride films or polysilicon films.

Examples of dispersing agents include vinyl alcohol polymers and theirderivatives, betaine, lauryl betaine, lauryldimethylamine oxide, and thelike. Examples of polishing rate improvers include β-alanine betaine,stearyl betaine, and the like. Examples of flattening agents that reduceirregularities on polished surfaces include ammonium lauryl sulfate,triethanolamine polyoxyethylene alkyl ether sulfate, and the like.Examples of global flattening agents include polyvinylpyrrolidone,polyacrolein, and the like. Examples of selective ratio improversinclude polyethyleneimine, polyallylamine, chitosan, and the like. Thesemay be used alone or in combinations of two or more.

The polishing liquid of this embodiment preferably comprises a vinylalcohol polymer or a derivative thereof as an additive. However, vinylalcohol, which is the monomer of polyvinyl alcohol, generally tend notto exist alone as a stable compound. Therefore, polyvinyl alcohol isusually obtained by polymerization of a vinyl carboxylate monomer suchas vinyl acetate monomer to obtain poly(vinyl carboxylate), followed bysaponification (hydrolysis). Thus, a vinyl alcohol polymer obtainedusing vinyl acetate monomer as the starting material has —OCOCH₃ andhydrolyzed —OH groups as functional groups in the molecule, and theproportion of —OH groups is defined as the saponification degree. Thatis, a vinyl alcohol polymer whose saponification degree is not 100% hasa structure which is essentially a copolymer of vinyl acetate and vinylalcohol. The vinyl alcohol polymer may be one in which a vinylcarboxylate monomer such as vinyl acetate monomer and other vinylgroup-containing monomer (for example, ethylene, propylene, styrene orvinyl chloride) are copolymerized, and all or some of the portionsderived from the vinyl carboxylate monomer are saponified. Thedefinition of the term “vinyl alcohol polymer” in this inventionencompasses all of these polymers, and it also may be considered to be apolymer having the following structural formula.

(wherein n represents a positive integer)

The definition of the term “derivative” of a vinyl alcohol polymerincludes a derivative of a homopolymer of vinyl alcohol (that is, apolymer with a saponification degree of 100%), and a derivative of acopolymer of a vinyl alcohol monomer and other vinyl group-containingmonomer.

Examples of the aforementioned derivatives include polymers having aportion of the hydroxyl groups substituted with amino, carboxyl or estergroups for example, and polymers having a portion of the hydroxyl groupsmodified. Examples of such derivatives include reactive polyvinylalcohols (for example, GOHSEFIMER (registered trademark) Z by NipponSynthetic Chemical Industry Co., Ltd.), cationized polyvinyl alcohols(for example, GOHSEFIMER (registered trademark) K by Nippon SyntheticChemical Industry Co., Ltd.), anionized polyvinyl alcohols (for example,GOHSERAN (registered trademark) L and GOHSENOL (registered trademark) Tby Nippon Synthetic Chemical Industry Co., Ltd.), and hydrophilicgroup-modified polyvinyl alcohols (for example, ECOMATI by NipponSynthetic Chemical Industry Co., Ltd.).

As mentioned above, vinyl alcohol polymers and their derivativesfunction as dispersing agents for abrasive grains, and have effects ofimproving polishing liquid stability. It is believed that interactionbetween the hydroxyl groups of the vinyl alcohol polymer or itsderivative and tetravalent metal hydroxide particles can inhibitaggregation and minimize changes of particle size in the polishingliquid, thereby improving stability. Also, the vinyl alcohol polymer andits derivative function as a selective ratio improver for the abrasivegrains, and when used in combination with tetravalent cerium hydroxideparticles, it can increase the polishing selective ratio for inorganicinsulating films (for example, silicon oxide films) with respect tostopper films (for example, polysilicon films) (polishing rate forinorganic insulating films/polishing rate for stopper films). Inaddition, a vinyl alcohol polymer and its derivative may also functionas a flattening agent or as an anti-adhesion agent for the abrasivegrains on the polished surface (cleanability improver).

The saponification degree of the vinyl alcohol polymer or its derivativeis preferably not greater than 95 mol % from the viewpoint of furtherincreasing the polishing selective ratio for inorganic insulating filmswith respect to stopper films. From the same viewpoint, thesaponification degree is more preferably not greater than 90 mol %, evenmore preferably not greater than 88 mol %, especially preferably notgreater than 85 mol %, extremely preferably not greater than 83 mol %and very preferably not greater than 80 mol %.

There are no particular restrictions on the lower limit for thesaponification degree, but from the viewpoint of excellent solubility inwater, it is preferably 50 mol % or greater, more preferably 60 mol % orgreater and even more preferably 70 mol % or greater. The saponificationdegree of the vinyl alcohol polymer and its derivative can be measuredaccording to JIS K 6726 (Polyvinyl alcohol test method).

The upper limit for the mean polymerization degree (weight-averagemolecular weight) of the vinyl alcohol polymer and its derivative is notparticularly restricted, but from the viewpoint of inhibiting reductionin polishing rate for inorganic insulating films (for example, siliconoxide films), it is preferably not greater than 50000, more preferablynot greater than 30000 and even more preferably not greater than 10000.

From the viewpoint of further increasing the polishing selective ratiofor inorganic insulating films with respect to stopper films, the lowerlimit for the mean polymerization degree is preferably 50 or greater,more preferably 100 or greater and even more preferably 150 or greater.The mean polymerization degree of the vinyl alcohol polymer and itsderivative can be measured according to JIS K 6726

(Polyvinyl Alcohol Test Method).

In order to adjust the polishing selective ratio for inorganicinsulating films with respect to stopper films, and the flatness ofpolished substrates, a plurality of polymers with differentsaponification degrees or mean polymerization degrees may be used incombination. In the case of different saponification degrees, thesaponification degree of at least one vinyl alcohol polymer or itsderivative is preferably not greater than 95 mol %, and for theviewpoint of improving the polishing selective ratio, the averagesaponification degree calculated from each saponification degree and themixing ratio is preferably not greater than 95 mol %. The preferredvalues for these saponification degrees are as specified above.

From the viewpoint of inhibiting excessive reduction in the polishingrate and improving the polishing selective ratio for inorganicinsulating films with respect to stopper films, the content of theadditive is preferably 0.01 mass % or greater, more preferably 0.1 mass% or greater, even more preferably 0.3 mass % or greater and especiallypreferably 0.5 mass % or greater based on the total mass of thepolishing liquid, when the slurry and additive liquid are mixed toproduce the polishing liquid. From the viewpoint of further inhibitingreduction in the polishing rate for inorganic insulating films, thecontent of the additive is preferably not greater than 10 mass %, morepreferably not greater than 5 mass % and even more preferably notgreater than 3 mass % based on the total mass of the polishing liquid.When at least one type of vinyl alcohol polymer or its derivative isused as an additive, the total content of the vinyl alcohol polymer andits derivative is preferably in the range specified above.

The content of the additive in the additive liquid is preferably 0.02-20mass % based on the total mass of the additive liquid, as this willallow the content of the additive in the polishing liquid to be easilyadjusted to within the range specified above.

(One-Pack Polishing Liquid)

The polishing liquid of this embodiment may be stored as a one-packpolishing liquid in a state that the slurry and additive of thepolishing liquid set are pre-mixed. Storage as a one-pack polishingliquid can eliminate the labor of mixing the slurry and additive liquidbefore polishing. In addition, storage as a one-pack polishing liquidwith pre-adjustment of the water content for polishing can eliminate thelabor of adjusting the concentration. The pH of the one-pack polishingliquid and the mean particle size R2 of the abrasive grains preferablysatisfy the numerical ranges specified for the polishing liquid to beobtained from a polishing liquid set.

For storage as a one-pack polishing liquid as well, the rate of changeof the mean particle size of the abrasive grains is preferably notgreater than 30%, more preferably not greater than 20% and even morepreferably not greater than 10%, as explained for the polishing liquidset.

In the case of a one-pack polishing liquid, the mean particle size R1 ofthe abrasive grains in the slurry can be determined in the followingmanner. Specifically, the one-pack polishing liquid is subjected to amethod such as repeated solid-liquid separation by centrifugalseparation or the like, for through washing and isolation of theabrasive grains. Next, the isolated abrasive grains are added to waterand subjected to ultrasonic dispersion for 2 minutes or longer in orderto obtain a slurry. The obtained slurry may be measured by the methoddescribed above to determine the mean particle size R1.

(Substrate Polishing Method)

The substrate polishing method using a polishing liquid set or one-packpolishing liquid of this embodiment will now be described.

In the substrate polishing method of this embodiment, polishing isperformed on a substrate having an inorganic insulating film (forexample, a silicon oxide film) as a film to be polished on its surface.The substrate polishing method of this embodiment comprises at least asubstrate positioning step and a polishing step. In the substratepositioning step, a film to be polished, of a substrate which has thefilm to be polished on its surface, is placed so as to face an abrasivepad. The silicon oxide film, as the inorganic insulating film, may beobtained by low-pressure CVD method, plasma CVD, or the like.

In the polishing step, when using a one-pack polishing liquid, at leasta portion of the inorganic insulating film is polished, in a state thatthe inorganic insulating film of the substrate is pressed against theabrasive pad of the polishing platen, by relatively moving the substrateand the polishing platen while supplying the polishing liquid betweenthe abrasive pad and the inorganic insulating film. Here, the polishingliquid may be supplied directly as a polishing liquid with theprescribed water content, or it may be supplied as a concentrate with alow water content and diluted on the abrasive pad.

When a polishing liquid set is used, there may be provided a polishingliquid preparation step in which the slurry and additive liquid aremixed before the polishing step to obtain a polishing liquid. In thiscase, in the polishing step, the polishing liquid obtained in thepolishing liquid preparation step is used to polish the inorganicinsulating film,

and specifically, the polishing liquid obtained in the polishing liquidpreparation step is supplied between the abrasive pad of the polishingplaten and the inorganic insulating film of the substrate with theinorganic insulating film pressed against the abrasive pad, whilerelatively moving the substrate and the polishing platen to polish atleast a portion of the inorganic insulating film. In this type ofpolishing method, the polishing liquid may be supplied onto the abrasivepad in the polishing liquid preparation step, after conveying the slurryand additive liquid through separate tubings (liquid conveyance systems)and merging the tubings for mixture just before the supply tubing outletto prepare the polishing liquid. The polishing liquid may also besupplied directly as a polishing liquid with the prescribed watercontent, or it may be supplied as a concentrate with a low water contentand diluted on the abrasive pad.

When a polishing liquid set is used, in the polishing step, at least aportion of the inorganic insulating film may be polished using thepolishing liquid obtained by mixing the slurry and additive liquid,while supplying each of the slurry and additive liquid between theabrasive pad and the inorganic insulating film. In this type ofpolishing method, the slurry and additive liquid may be supplied ontothe abrasive pad through separate tubings (liquid conveyance systems).Also, the slurry and/or additive liquid may be supplied as concentrateswith low water contents, and diluted on the abrasive pad.

According to this embodiment, a substrate may be polished using a slurryinstead of a one-pack polishing liquid. In this case, in the polishingstep, at least a portion of the inorganic insulating film is polished,in a state that the inorganic insulating film of the substrate ispressed against the abrasive pad of the polishing platen, by relativelymoving the substrate and the polishing platen while supplying the slurrybetween the abrasive pad and the inorganic insulating film.

The polishing apparatus to be used in the polishing method of thisembodiment may be, for example, a common polishing apparatus comprisinga holder that holds the substrate with the film to be polished, and apolishing platen which allows attachment of an abrasive pad and mounts amotor having a variable rotational speed. Examples of such polishingapparatuses include the model EPO-111 which is polishing apparatus byEbara Corp., and Mirra3400 and Reflection polishing machines (tradenames) which are polishing apparatuses by Applied Materials.

There are no particular restrictions on the abrasive pad, and a commonnonwoven fabric, foamed polyurethane pad, porous fluorine resin pad orthe like may be used. The abrasive pad is preferably furrowed to allowaccumulation of the polishing liquid.

The polishing conditions are not particularly restricted, but from theviewpoint of minimizing fly off of the semiconductor substrate, therotational speed of the polishing platen is preferably a low speed ofnot greater than 200 rpm. The pressure (machining load) on thesemiconductor substrate is preferably not greater than 100 kPa, from theviewpoint of further inhibiting formation of scratches on the polishedsurface. The polishing liquid is preferably continuously supplied to thesurface of the abrasive pad with a pump or the like during polishing.The amount supplied is not particularly restricted, but the surface ofthe abrasive pad is preferably covered by the polishing liquid at alltimes. Preferably, the polished semiconductor substrate is thoroughlyrinsed in running water, and is then dried after removing off the waterdroplets adhering to the semiconductor substrate using a spin dryer orthe like.

EXAMPLES

The present invention will now be described in greater detail byexamples, with the understanding that the invention is not limited tothese examples.

Example 1

<Preparation of Slurry>

A 400 g portion of Ce(NH₄)₂(NO₃)₆ was dissolved in 7500 g of water toobtain a metal salt aqueous solution. Next, 210 g of ammonia water (25mass% aqueous solution) was added to the metal salt aqueous solution ata mixing rate of 30 cc/min, and the mixture was stirred at 200 rpm toobtain a slurry comprising cerium hydroxide particles (abrasive grains).The liquid temperature of the metal salt aqueous solution and ammoniawater was 25° C. Next, the slurry was subjected to solid-liquidseparation by centrifugal separation to remove the liquid, then freshwater was added and ultrasonic dispersion treatment was conducted. Thelight transmittance for a wavelength of 500 nm was 61%/cm in the slurry(aqueous dispersion) adjusted to an abrasive grain content of 1.0 mass%. The mean particle size R1 of the secondary particles was 105 nm, asmeasured by a photon correlation method using the slurry adjusted to anabrasive grain content of 0.2 mass %. The pH of the slurry, as measuredusing a Model PH81 by Yokogawa Electric Corp., was 3.8.

<Preparation of Polishing Liquid>

A polishing liquid was prepared by mixing and stirring 60 g of theslurry with the abrasive grain content adjusted to 1 mass %, 60 g of apolyvinyl alcohol aqueous solution adjusted to 5 mass %, and 180 g ofpurified water. The mean particle size R2 of the secondary particles was132 nm, as measured by a photon correlation method using this polishingliquid. The pH of the polishing liquid, as measured using a Model PH81by Yokogawa Electric Corp., was 6.3. The polyvinyl alcohol used was avinyl alcohol polymer with a saponification degree of 80 mol % and amean polymerization degree of 300. The same vinyl alcohol polymer wasused in the following examples and comparative examples.

<Polishing of Insulating Film>

A φ200 mm silicon wafer, with a silicon oxide (SiO₂) insulating filmformed thereon, was set in a polishing apparatus holder mounting anadsorption pad for substrate attachment. The holder was placed on theporous urethane resin pad-mounted platen with the insulating filmsurface facing downward, the previously obtained polishing liquid(abrasive grain content: 0.2 mass %) was supplied onto the pad at asupplied amount of 200 cc/min, and the wafer was pressed at a polishingload of 20 kPa. Polishing was performed by 1 minute of rotation of theplaten at 78 rpm and the holder at 98 rpm. The polished wafer wasthoroughly washed with purified water and dried. A light-interferencefilm thickness meter was used to measure the change in film thicknessbefore and after polishing, and the result indicated a polishing amountof 210 nm.

<Polishing of Stopper Film>

A φ200 mm silicon wafer, with a polysilicon (p-Si) film formed thereon,was set in a polishing apparatus holder mounting an adsorption pad forsubstrate attachment. The holder was placed on the porous urethane resinpad-mounted platen with the insulating film surface facing downward, thepreviously obtained polishing liquid (abrasive grain content: 0.2 mass%) was supplied onto the pad at a supplied amount of 200 cc/min, and thewafer was pressed at a polishing load of 20 kPa. Polishing was performedby 1 minute of rotation of the platen at 78 rpm and the holder at 98rpm. The polished wafer was thoroughly washed with purified water anddried. A light-interference film thickness meter was used to measure thechange in film thickness before and after polishing, and the resultindicated a polishing amount of 1.9 nm.

Example 2

<Preparation of Slurry>

A 40 g portion of Ce(NH₄)₂(NO₃)₆ was dissolved in 1200 g of water toobtain a metal salt aqueous solution. Next, 45 g of ammonia water (12mass% aqueous solution) was added to the metal salt aqueous solution ata mixing rate of 20 cc/min, and the mixture was stirred at 200 rpm toobtain a slurry comprising cerium hydroxide particles (abrasive grains).The liquid temperature of the metal salt aqueous solution and ammoniawater was 25° C. Next, the slurry was subjected to solid-liquidseparation by centrifugal separation to remove the liquid, then freshwater was added and ultrasonic dispersion treatment was conducted. Thelight transmittance for a wavelength of 500 nm was 91%/cm in the slurry(aqueous dispersion) adjusted to an abrasive grain content of 1.0 mass%. The mean particle size R1 of the secondary particles was 101 nm, asmeasured by a photon correlation method using the slurry adjusted to anabrasive grain content of 0.2 mass %. The pH of the slurry, as measuredusing a Model PH81 by Yokogawa Electric Corp., was 3.6.

<Preparation of Polishing Liquid>

A polishing liquid was prepared by mixing and stirring 60 g of theslurry with the abrasive grain content adjusted to 1 mass %, 60 g of apolyvinyl alcohol aqueous solution adjusted to 5 mass %, and 180 g ofpurified water. The mean particle size R2 of the secondary particles was110 nm, as measured by a photon correlation method using this polishingliquid. The pH of the polishing liquid, as measured using a Model PH81by Yokogawa Electric Corp., was 6.4.

<Polishing of Insulating Film>

Using the previously obtained polishing liquid (abrasive grain content:0.2 mass %), a silicon oxide insulating film and polysilicon film weresubjected to polishing, washing and drying in the same manner as Example1, and the change in film thickness before and after polishing wasmeasured. The polishing amount of the silicon oxide film was 290 nm, andthe polishing amount of the polysilicon film was 2.2 nm.

Example 3

<Preparation of Slurry>

A 200 g portion of Ce(NH₄)₂(NO₃)₆ was dissolved in 7500 g of water toobtain a metal salt aqueous solution. Next, 220 g of ammonia water (12mass% aqueous solution) was added to the metal salt aqueous solution ata mixing rate of 5 cc/min, and the mixture was stirred at 500 rpm toobtain a slurry comprising cerium hydroxide particles (abrasive grains).The liquid temperature of the metal salt aqueous solution and ammoniawater was 20° C. Next, the slurry was subjected to solid-liquidseparation by centrifugal separation to remove the liquid, then freshwater was added and ultrasonic dispersion treatment was conducted. Thelight transmittance for a wavelength of 500 nm was 92%/cm in the slurry(aqueous dispersion) adjusted to an abrasive grain content of 1.0 mass%. The mean particle size R1 of the secondary particles was 72 nm, asmeasured by a photon correlation method using the slurry adjusted to anabrasive grain content of 0.2 mass %. The pH of the slurry, as measuredusing a Model PH81 by Yokogawa Electric Corp., was 3.8.

<Preparation of Polishing Liquid>

A polishing liquid was prepared by mixing and stirring 60 g of theslurry with the abrasive grain content adjusted to 1 mass %, 60 g of apolyvinyl alcohol aqueous solution adjusted to 5 mass %, and 180 g ofpurified water. The mean particle size R2 of the secondary particles was78 nm, as measured by a photon correlation method using this polishingliquid. The pH of the polishing liquid, as measured using a Model PH81by Yokogawa Electric Corp., was 6.3.

<Polishing of Insulating Film>

Using the previously obtained polishing liquid (abrasive grain content:0.2 mass %), a silicon oxide insulating film and polysilicon film weresubjected to polishing, washing and drying in the same manner as Example1, and the change in film thickness before and after polishing wasmeasured. The polishing amount of the silicon oxide film was 320 nm, andthe polishing amount of the polysilicon film was 2.5 nm.

Comparative Example 1

<Preparation of Slurry>

A 430 g portion of Ce(NH₄)₂(NO₃)₆ was dissolved in 7300 g of water toobtain a metal salt aqueous solution. Next, 240 g of ammonia water (25mass% aqueous solution) was added to the metal salt aqueous solution ata mixing rate of 80 cc/min, and the mixture was stirred at 200 rpm toobtain a slurry comprising cerium hydroxide particles (abrasive grains).The liquid temperature of the metal salt aqueous solution and ammoniawater was 25° C. Next, the slurry was subjected to solid-liquidseparation by centrifugal separation to remove the liquid, then freshwater was added and ultrasonic dispersion treatment was conducted. Thelight transmittance for a wavelength of 500 nm was 43%/cm in the slurry(aqueous dispersion) adjusted to an abrasive grain content of 1.0 mass%. The mean particle size R1 of the secondary particles was 115 nm, asmeasured by a photon correlation method using the slurry adjusted to anabrasive grain content of 0.2 mass %. The pH of the slurry, as measuredusing a Model PH81 by Yokogawa Electric Corp., was 3.9.

<Preparation of Polishing Liquid>

A polishing liquid was prepared by mixing and stirring 60 g of theslurry with the abrasive grain content adjusted to 1 mass %, 60 g of apolyvinyl alcohol aqueous solution adjusted to 5 mass %, and 180 g ofpurified water. The mean particle size R2of the secondary particles was163 nm, as measured by a photon correlation method using this polishingliquid. The pH of the polishing liquid, as measured using a Model PH81by Yokogawa Electric Corp., was 6.5.

<Polishing of Insulating Film>

Using the previously obtained polishing liquid (abrasive grain content:0.2 mass %), a silicon oxide insulating film and polysilicon film weresubjected to polishing, washing and drying in the same manner as Example1, and the change in film thickness before and after polishing wasmeasured. The polishing amount of the silicon oxide film was 120 nm, andthe polishing amount of the polysilicon film was 1.6 nm.

The synthesis conditions for the abrasive grains and the values of theproperties of the slurries and polishing liquids in Examples 1-3 andComparative Example 1 are shown in Table 1.

TABLE 1 Example 1 Example 2 Example 3 Comp. Ex. 1 Synthesis Metal saltCerium salt 400 g 40 g 200 g 430 g conditions solution Water 7500 g 1200g 7500 g 7300 g Concentration 0.097 mol/L 0.061 mol/L 0.049 mol/L 0.107mol/L Alkali solution Ammonia water 25 mol/L 12 mol/L 12 mol/L 25 mol/L210 g 45 g 220 g 240 g Mixing speed 30 cc/min 20 cc/min 5 cc/min 80cc/min Stirring speed 200 rpm 200 rpm 500 rpm 200 rpm Liquid temperature25° C. 25° C. 20° C. 25° C. Properties Light transmittance (%/cm) 61 9192 43 pH of slurry 3.8 3.6 3.8 3.9 pH of polishing liquid 6.3 6.4 6.36.5 Secondary particle size in slurry 105 101 72 115 (R1[nm]) Secondaryparticle size in polishing 132 110 78 163 liquid (R2[nm]) Change rate ofsecondary particle 26 9 8 42 size [%] SiO₂ polishing rate [nm/min] 210290 320 120 p-Si polishing rate [nm/min] 1.9 2.2 2.5 1.6 Polishingselectivity (SiO₂/p-Si) 111 132 128 75

It was then examined how the polishing rate varied when changing thepolyvinyl alcohol (PVA) contents for preparation of polishing liquids,using the slurries of Example 1 and Comparative Example 1. Specifically,the polishing rates for silicon oxide films were examined in the samemanner as Example 1, with polyvinyl alcohol contents of 3 mass %, 2 mass%, 1 mass %, 0.5 mass % and 0.1 mass % in the polishing liquid. Theresults are shown in Table 2 and FIG. 3.

TABLE 2 PVA content (mass %) 3 2 1 0.5 0.1 Polishing rate Example 1 54135 210 240 270 (nm/min) Comp. Ex. 1 3 57 120 150 180

As clearly shown by the results in Table 1, it was confirmed that it waseasily possible to achieve both the addition effect of additive and theeffect of improving polishing rate for the film to be polished, inExamples 1-3 which had light transmittances of at least 50%/cm for lightwith a wavelength of 500 nm. Also, as clearly shown by the results inTable 2 and FIG. 3, the polishing rate in Example 1, which had a lighttransmittance of at least 50%/cm for light with a wavelength of 500 nm,was higher than in Comparative Example 1 with addition of additives inthe same amount, and therefore a margin exists for further addition ofadditives, in addition to polyvinyl alcohol. This indicates that furtherproperties can be imparted by adding more additives in Example 1. Thereason for the high polishing rate with such a high light transmittanceis believed to be due to the small difference in mean particle sizebetween the slurry and polishing liquid in the case of high lighttransmittance, in contrast to a tendency toward greatly increased meanparticle size of the abrasive grains in the polishing liquid compared tothe mean particle size of the abrasive grains in the slurry, in the caseof low light transmittance.

The invention claimed is:
 1. A slurry comprising abrasive grains andwater, the abrasive grains including particles comprising a hydroxide oftetravalent cerium, the abrasive grains producing light transmittance ofat least 50%/cm for light with a wavelength of 500 nm in an aqueousdispersion with a content of the abrasive grains adjusted to 1.0 mass %.2. The slurry according to claim 1, wherein a mean particle size of theabrasive grains is 1-150 nm.
 3. The slurry according to claim 1, whereina pH is 2.0-9.0.
 4. The slurry according to claim 1, wherein a contentof the abrasive grains is 0.01-15 mass % based on a total mass of theslurry.
 5. The slurry according to claim 1, wherein a content of theparticles comprising a hydroxide of tetravalent cerium is 0.01-10 mass %based on a total mass of the slurry.
 6. The slurry according to claim 1,wherein the abrasive grains are composed of the particles comprising ahydroxide of tetravalent cerium.
 7. A polishing liquid set comprisingconstituent components of a polishing liquid separately stored as afirst liquid and a second liquid, so that the first liquid and secondliquid are mixed to form the polishing liquid, wherein the first liquidis the slurry according to claim 1, and the second liquid comprises anadditive and water.
 8. The polishing liquid set according to claim 7,wherein a mean particle size of the abrasive grains in the polishingliquid is 1-200 nm.
 9. The polishing liquid set according to claim 7,wherein a mean particle size R1 of the abrasive grains in the firstliquid and a mean particle size R2 of the abrasive grains in thepolishing liquid satisfy the following formula (1).|R1−R2|/R1×100≤30  (1)
 10. The polishing liquid set according to claim7, wherein the additive is at least one type selected from amongdispersing agents, polishing rate improvers, flattening agents andselective ratio improvers.
 11. The polishing liquid set according toclaim 7, wherein the additive is a vinyl alcohol polymer and/or a vinylalcohol polymer derivative.
 12. The polishing liquid set according toclaim 7, wherein a content of the additive in the polishing liquid is0.01 mass % or greater based on a total mass of the polishing liquid.13. A polishing liquid comprising abrasive grains, an additive andwater, the abrasive grains including particles comprising a hydroxide oftetravalent cerium, the abrasive grains producing light transmittance ofat least 50%/cm for light with a wavelength of 500 nm in an aqueousdispersion with a content of the abrasive grains adjusted to 1.0 mass %.14. The polishing liquid according to claim 13, wherein a content of theparticles comprising a hydroxide of tetravalent cerium is 0.01-8 mass %based on a total mass of the polishing liquid.
 15. The polishing liquidaccording to claim 13, wherein a mean particle size of the abrasivegrains is 1-200 nm.
 16. The polishing liquid according to claim 13,wherein a pH is 3.0-9.0.
 17. The polishing liquid according to claim 13,wherein the additive is at least one type selected from among dispersingagents, polishing rate improvers, flattening agents and selective ratioimprovers.
 18. The polishing liquid according to claim 13, wherein theadditive is a vinyl alcohol polymer and/or a vinyl alcohol polymerderivative.
 19. The polishing liquid according to claim 13, wherein acontent of the additive is 0.01 mass % or greater based on a total massof the polishing liquid.
 20. A substrate polishing method comprising: astep of placing a film to be polished, of a substrate which has the filmto be polished on its surface, so as to face an abrasive pad, and a stepof polishing at least a portion of the film to be polished whilesupplying the polishing liquid according to claim 13 between theabrasive pad and the film to be polished.
 21. A substrate polishingmethod comprising: a step of placing a film to be polished, of asubstrate which has the film to be polished on its surface, so as toface an abrasive pad, a step of mixing the first liquid and secondliquid of the polishing liquid set according to claim 7 to obtain thepolishing liquid, and a step of polishing at least a portion of the filmto be polished while supplying the polishing liquid between the abrasivepad and the film to be polished.
 22. A substrate polishing methodcomprising: a step of placing a film to be polished, of a substratewhich has the film to be polished on its surface, so as to face anabrasive pad, and a step of polishing at least a portion of the film tobe polished while supplying both the first liquid and second liquid ofthe polishing liquid set according to claim 7 between the abrasive padand the film to be polished.
 23. A substrate polishing methodcomprising: a step of placing a film to be polished, of a substratewhich has the film to be polished on its surface, so as to face anabrasive pad, and a step of polishing at least a portion of the film tobe polished while supplying the slurry according to claim 1 between theabrasive pad and the film to be polished.
 24. The slurry according toclaim 1, wherein a pH is 3.0-6.0, and a mean particle size of theabrasive grains is 5-120 nm.
 25. The polishing liquid according to claim13, wherein a pH is 5.0-8.0, and a mean particle size of the abrasivegrains is 15-150 nm.